The present invention relates generally to connectors for optical fibers and devices. In particular, the present invention relates to an optical connector including a rounded rod alignment feature.
Optical fibers are increasingly being used for the transmission of optical signals. Optical fibers offer greatly increased transmission capability and transmission characteristics over traditional copper wires.
The use of optical fibers, however, does present some difficulties. Optical fibers are, in fact, conductors of light signals. To avoid losing or degrading the light signals being transmitted, there is a need for precise alignment and coupling any time optical fibers are connected to each other or to optical devices. Optic transfer efficiency is the term used to measure the ability of a connector to accurately couple the transmitted light signals.
Use of optical cables has generally been limited to large scale long haul trunking installations, such as those of the telecommunications industry, where the improved transmission characteristics of the optical fibers justify the greater expense and typical difficulty associated with their manufacturing and installation. Nevertheless, as demands on communication media and data volume continue to increase, the advantages of using optical cable for transmission of signals across shorter distances, or for interconnecting local devices, continues to grow. With this growth has come a need to connect fiber optic cables accurately and economically to each other and to a multiplicity of devices.
Of considerable relevance to the problem of developing practical fiber optic connectors is the question of the optic transfer efficiency at the connector. Various factors affect the optic transfer efficiency at a connector including (a) gap separation at the point of abutment, (b) lateral separation due to axial misalignment, and (c) thermal expansion characteristics of connectors.
Numerous optical cable connectors have been developed to aid in the connection of fiber optic cables. As data requirements grow, single fiber cables have given way to multiple fiber cables, such as parallel ribbon cables including a plurality of optical fibers aligned in parallel. As the number of fibers grow, such do the difficulties in maintaining the transfer efficiency of the connector.
Examples of known multi-fiber connectors include the MAC(trademark) connector by Berg Electronics and the MT Connector by U.S. Conec. Further examples of optical connectors are illustrated in U.S. Pat. No. 5,420,952 to Katsura, et al.; U.S. Pat. No. 5,276,755 to Longhurst; U.S. Pat. No. 5,500,915 to Foley et al.; U.S. Pat. No. 4,784,457 to Finzell; U.S. Pat. No. 5,430,819 to Sizer, II, et al.; and U.S. Pat. No. 5,287,426 to Shahid.
Many of the known connectors have disadvantages associated with them. A MT-type connector, illustrated in FIG. 1, is one of the most common connectors currently used. Connector 10 includes a ferrule 12 having two protruding long pins 20 and 22. The proposed TIA/EIA-604-5 MT connector intermateability standard specifies that the alignment pins must protrude at least 2.285 pin diameters (1.6 mm protrusion for a 0.7 mm diameter pin) from the face of the ferrule.
Long thin pins, such as those of the MT connector, attempt to control movement of the connector in the x, y and z axis. Long pins may help achieve suitable optical connections for some applications and the coupling of pins and holes may be intuitive to users. However, the use of such long pins does present significant coupling, alignment, durability and manufacturing disadvantages.
As illustrated in FIGS. 2 and 3, during coupling of a MT-type connector, the ferrule 12 is interference fit upon a receptacle 14. The receptacle 14 defines a receiving orifice or hole 30. The pin 20 is inserted into the corresponding receiving hole 30. Significant insertion force is needed to seat each small diameter (xcx9c0.7 mm) pin fully into the respective hole. It has been calculated that the interference fit of a nominal MT connector pin inserted into a matching receptacle hole could require approximately six Newtons of force to fully seat. If the pins are not fully seated, an air gap between the two ferrules results that can cause severe light loss.
Correct alignment of the pins is very important before coupling. FIG. 2 illustrates a 0.5 mm lateral misalignment of the 0.7 mm MT connector pin 20. The small diameter of the pin 20 and of the matching receiving hole 30 results in complete failure to couple even under very small (e.g., half a millimeter) lateral misalignment.
FIG. 3 illustrates the effects of angular misalignment of pin 20. As the effects of even a small angular misalignment are magnified by the length of the pin, even a small angular misalignment (5 degrees) may again result in complete failure to couple.
If the pin 20 is not perfectly aligned before engagement into the mating hole 30, the pin 20 may miss the hole 30 and crack the mating ferrule 14 causing a catastrophic failure. The long and thin metal pins 20 and 22 also are liable to bend during insertion and withdrawal and damage the mating ferrule 14 on subsequent insertions. The high interference fit of the long pin to the mating hole can cause the hole to be xe2x80x9cskivedxe2x80x9d and deposit unwanted debris onto the connector mating face which can cause signal failure. Because the pins protrude so far from the mating face of the MT, the mating face is difficult to clean.
Manufacture of a MT connector further requires tight control of the tolerances of at least nine critical dimensions: (1) pin diameter, (2) pin straightness, (3) pin taper, (4) hole diameter, (5) hole straightness, (6) hole angle, (7) hole taper, (8) hole placement relative to matching hole, (9) hole placement relative to fibers. Accordingly, the use of traditional alignment pins further drives up manufacturing difficulty and costs.
A further consideration is that the long protruding metal MT alignment pins have a tendency to act as xe2x80x9cantennasxe2x80x9d and may cause electro-magnetic interference when placed near high frequency components. This interference may in turn cause signal interference to other equipment and components.
An alternative optical connector design is disclosed in U.S. Pat. No. 5,778,123, entitled xe2x80x9cAlignment Assembly for Multifiber or Single Fiber Optical Cable Connectorxe2x80x9d, commonly assigned with the present invention to Minnesota Mining and Manufacturing and which is hereby incorporated by reference. The patent discloses a xe2x80x9cball and socketxe2x80x9d alignment structure, illustrated in FIG. 4, where an opening or socket 130 in a ferrule 100 seats a ball 120, rather than a long pin. The opening 130 has a depth d1. The ball 120 has a radius R, where R greater than d1. The ball and socket structure offers significant advantages as the design does not overconstrain the z-axis alignment and requires control of only two manufacturing tolerances: the size of the alignment ball, which is easily controllable, and the spacing between the two openings.
However, the ball 120 offers only a limited bonding surface to the associated alignment hole 130. A limited bonding surface may result in inadequate bonding of the ball 120 to the ferrule 100. Also, the ball and socket design may be susceptible to damage from overpolishing of the ferrule and fiber ends. As illustrated in FIG. 5, overpolishing a ball-in-socket ferrule face may damage or obliterate the ball alignment opening or chamfer, thus inhibiting accurate attachment of the ball.
The opportunity remains for an improved optical connector and alignment feature.
The present invention is a fiber optic connector including a novel alignment feature having improved alignment and manufacturing characteristics over traditional connectors, while offering the advantages of both the traditional pin connectors and the ball-in-socket connector. The connector includes large diameter alignment rods tightly fit into appropriately sized holes to align optical fiber cores and produce a low loss optical interconnection. Large diameter rods are defined as rods wherein the rods have a diameter such that the rods protrude from the containing holes less than two rod diameters.
A fiber optic connector of the present invention has a first connector ferrule and alignment means for aligning the first connector ferrule with a matching second connector ferrule. In an exemplary embodiment, the fiber optic connector includes a first connector ferrule including a first mating surface. The mating surface defines at least one receiving cavity, and at least one protruding alignment rod is seated in the cavity and extends from the mating surface. The alignment rod has a diameter D1 and protruded from the mating surface a protrusion distance p1, wherein p1xe2x89xa62D1. In an exemplary embodiment the rod has a hemispherical tip and 0.5D1xe2x89xa6p1xe2x89xa62D1.
The fiber optic connector may further include a second connector ferrule having a second mating surface configured to be aligned opposite the first connector ferrule. The second mating surface defines a second receiving cavity having a depth P2 wherein and p1 less than P2.
The second connector ferrule may further includes a second cavity and at least one second protruding alignment rod seated in the cavity, the alignment rod having a diameter d1 and protruding from the mating surface a protrusion distance p1, wherein p1 less than 2d1. In turn, the first mating surface of the first connector ferrule may define a second receiving cavity having a depth p2, wherein p1 less than p2, and wherein the first receiving cavity is configured to be aligned to receive the first alignment rod and the second receiving cavity is configured to be aligned to receive the second alignment rod.
The fiber optic connector may further include longitudinal grooves designed to receive at least one optical fiber. In an exemplary embodiment, the mating surfaces are positioned at a longitudinal end (defined by the direction of the optical fibers) of the connector ferrule.
In an alternative embodiment of the connector of the present invention, the connector ferrule defines a device-receiving cavity. An optoelectronic component is placed within the device-receiving cavity and a flexible circuit is electrically coupled to the optoelectronic component. In an exemplary embodiment, the flexible circuit encapsulates and protect the optoelectronic component within the receiving cavity. The flexible circuit may include at least one light-transmissive window optically aligned with the optoelectronic component.